1. Field of the Invention
The present invention relates to a method for discriminating an organic crop from a conventional crop, or an organic farmland from a conventional farmland by using a nitrogen isotope index in a soil sample or crop sample.
2. Description of the Related Art
In conventional cultivation practice, an excess amount of chemical fertilizer and pesticides have been used to increase the production yield. However, those chemical fertilizer and pesticides have caused ecological disturbance such as accumulation of salts and imbalance of nutrients in soil, decrease in the number of soil microorganisms and natural predators; water contamination; and safety problems in agricultural products, etc. With respect to these problems, it is anticipated that international trade volume in organic crop will be increased by way of international efforts to link agriculture, environment and trade, and thus to make international regulations to resolve the above problems. Further, a standard for an organic crop will be set up in Codex. OECD is planning to evaluate agricultural policies of each country by developing environmental index of agriculture in 13 divisions.
In response to these international efforts, “Law for promoting environmentally favorable agriculture” and “enforcement Law thereof” have been made in Korea to promote agriculture in an environmentally favorable way and to promote the production of value-added agricultural products by introducing a quality certification system therefor. According to the standard adopted in the quality certification system for environmentally favorable agricultural products, i.e., Quality Standard for crop (Korea), agricultural products are classified into four categories: low-pesticide agricultural products (the amount of used synthesized pesticide is ½ or lower of the standard amount thereof and the amount of used chemical fertilizer is ½ or lower of the recommended amount thereof); pesticide free agricultural products (no use of synthesized pesticides and the amount of used chemical fertilizer is ⅓ or lower of the recommended amount thereof); transitional organic agricultural products (no use of synthesized pesticides more than 1 year and no use of chemical fertilizer); and organic agricultural products (no use of synthesized pesticides more than 3 years and no use of chemical fertilizer). Thus, it is critical to determine whether a synthesized pesticide or a chemical fertilizer has been used or not in evaluating agricultural products according to the quality certification system.
Synthesized pesticides can be investigated by monitoring residual pesticides in a crop or soil sample. On the contrary, chemical fertilizer can be investigated only by an indirect method such as data on farming and an analysis of chemical properties of corresponding soil. However, there were problems that data on farming may be arbitrarily made by a farmer, and although the chemical properties of soil are directly affected by the application rates of fertilizers thereto, there is no scientific relationship between the chemical properties of soil and a type of fertilizer (chemical fertilizer or organic fertilizer) applied thereto. According to the state of the art, it is impossible to objectively determine whether a chemical fertilizer or an organic fertilizer has been used in a soil. Thus, there is a need for a method for determining whether chemical fertilizer or organic fertilizer has been used in soil of interest. Such a method is also needed to satisfy the consumer's need to know whether an agricultural product of interest was grown with chemical fertilizer or organic fertilizer.
There has been an attempt to determine the source of water contamination on the basis that a nitrogen isotope ratio of chemical fertilizer is different from that of livestock manure (Kohl et al, 1971, Fertilizer nitrogen: contribution to nitrate in surface water in a corn belt watershed, Science 174: 1331-1334). An analysis for the nitrogen isotope was employed for the purpose of studying the source of water contamination (lqbal et al, 1997, Nitrogen isotope indicators of seasonal source variability to groundwater, Environmental Geology 32: 210-218). However, the analysis for nitrogen isotope has never been used to investigate the kind of fertilizer (chemical vs. organic) applied to a farmland or to discriminate a crop grown with organic fertilizer from a crop grown with a chemical fertilizer.
The inventors have statistically analyzed distribution of nitrogen isotope in chemical fertilizer and organic fertilizer, and carried out experiments to examine the effect of chemical fertilizer or organic fertilizer on the nitrogen isotope index of a soil and a crop therefrom, and completed the present invention.